Dipeptide (DP) is actually one molecule, which consists of 2 amino acids that are joined by a single peptide bond. Since it consists of 2 different amino acids, it can have different sequences, like Ala-Gly or Gly-Ala. Such dipeptides would have different chemical and biological properties. The matter is that if written left to right in Gly-Ala, the glycine has the 'free' amine terminal end, while alanine has the 'free' carboxyl acid terminal end.
Dipeptide can be produced in different ways, which are generally divided into 3 methods: chemical synthesis, chemoenzymatic synthesis, and enzymatic synthesis.
Meanwhile, the function of di-peptides can be viewed from two points: as a derivative of amino acid and as the dipeptide itself. The first one is quite easy to understand, since although DPs and the constitutive amino acids feature different physicochemical properties, they should still share the same physiological effects, because dipeptides are degraded into the individual amino acids in organisms.
For instance, L-Glutamine is heat labile, but L-alanyl-L-glutamine is more tolerant to heat. Another good example is solubility: while Tyr is practically insoluble, you can dissolve Ala-Tyr up to 14 g/L. The most interesting fact is that a number of dipeptides are more soluble than each of the constitutive amino acids. For example, the solubilities of Ala and Gln are 89 and 36 g/L accordingly, but that of Ala-Gln is 586 g/L! Considering these properties and the fact that Ala-Gln and Gly-Tyr are quickly degraded into the individual amino acids when taken into the body, these dipeptides are used as components of patient infusions.
A number of dipeptides feature really unique functions that you won't find in the constitutive amino acids. For example, Carnosine and the related DPs anserine have appeared to exist in many tissues of mammalian, bird, and fish origin. A lot of functions have been anticipated to such dipeptides, like antioxidation and maintenance of cellular pH. Since di peptides and their derivatives reflect such possible functions, they are used in many ways - in sport nutrition, for example, which is based on the fact that the muscle of a fastswimming fish contains the dipeptides in question in higher concentrations than anything else. Other compounds, like Zinc carnosine, can be used as an antiulcer drug, while N-acetyl carnosine is used as an agent for cataracts.
The taste of dipeptides has also been studied for a long time. The research into the taste of synthetic di-peptides revealed that most of them appeared to be bitter, and the relationship between their physicochemical properties and bitterness has attracted the attention of the researchers. If we consider commercial application, aspartame is the only DPs of outstanding importance. Today almost 20,000 tons of aspartame, which is hundreds of times sweeter than sugar, is consumed annually throughout the globe as a low-calorie sweetener.
Another thing that captured the researchers' attention was the antihypertensive effect of DPs. Extracts or hydrolysates of fish meat, seaweed, or mushrooms were found out to exert a blood pressure lowering effect, with the active agents being identified as a few kinds of dipeptides like Ile-Tyr, Ile-Trp, and Lys-Trp. Such effects of the dipeptides in question were considered to be derived from their inhibitory effect on angiotensin-I-converting enzyme. As a result, in Japan the extracts or hydrolysates with such dipeptides were approved as foods for specified health uses.
Aside from the DPs that are mostly applied in industry, there're a number of dipeptides that aren't used practically, but their functions are still well-known. For example, Kyotorphin was isolated from bovine brain to feature analgesic effects; a synthetic DP Lys-Glu was found to show antitumor activity, while Leu-Ile appeared to have a neuroprotective effect, and Tyr-Gly is known for enhancing proliferation of peripheral blood lymphocytes.
Finally, transport mechanisms for dipeptides and amino acids differ, which means that they may exert different nutritional impacts on your body if taken orally.